The present invention relates to an internal combustion engine control method and apparatus for preventing a control variable of an engine from pulsating when it is subjected to the operation of analog-to-digital conversion, and more particularly the invention relates to a control method and apparatus which repetitively corrects the analog-to-digital conversion interval in accordance with the number of the engine cylinders and the engine speed.
In a known type of internal combustion engine control method in which the control variables of an engine, such as, the cooling water temperature, intake air pressure and intake air flow of the engine are detected by various sensors and subjected to the operation of analog-to-digital conversion (hereinafter referred to as A/D conversion) thereby controlling the engine to obtain the optimum operating condition, the A/D conversion of the control variables are conventionally effected at predetermined intervals or in synchronism with the conversion capacity of an A/D converter.
Of the analog output signals of the control variables detected by the sensors, if the output signal of the control variable which pulsates in synchronism with the engine rotation (e.g., in a sine wave form as shown by the solid line in FIG. 5) is subjected to the A/D conversion according to the prior art method, the engine control variable subjected to the A/D conversion is caused to vary even when the engine is operating in a steady-state condition, for example. In extreme cases, the occurrence of a particular relationship between the pulsation period of the control variable and the A/D conversion period results in the generation of a surge which is so large as to cause a detrimental effect on the exhaust emission and the drivability. In such a condition, it is impossible to ensure a fine control of the engine.
Even if a filter is provided to remove the pulsation of the control variable, the reduction rate is limited from the standpoint of the response during the transitional period making it impossible to overcome the foregoing deficiencies.